98 research outputs found
Magnesium Chloride as a Leaching and Aragonite-promoting Self-regenerative Additive for the Mineral Carbonation of Calcium-rich Materials
Two approaches for the intensification of the mineral carbonation reaction are combined and studied in this work, namely: (i) the calcium leaching and aragonite promoting effects of magnesium chloride (MgCl2), and (ii) the passivating layer abrasion effect of sonication. The alkaline materials subjected to leaching and carbonation tests included lime, wollastonite, steel slags, and air pollution control (APC) residue. Batch leaching tests were conducted with varying concentrations of additives to determine extraction efficiency, and with varying solids-to-liquid ratios to determine solubility limitations. Aqueous mineral carbonation tests, with and without the use of ultrasound, were conducted applying varying concentrations of magnesium chloride and varying durations to assess CO2 uptake improvement and characterize the formed carbonate phases. The leaching of calcium from lime with the use of MgCl2 was found to be atomefficient (1 mol Ca extracted for every mole Mg added), but the extraction efficiency from slags and APC residue was limited to 26–35 % due to mineralogical and microstructural constraints. The addition of MgCl2 notably improved argon oxygen decarburization (AOD) slag carbonation extent under sonication, where higher additive dosage resulted in higher CO2 uptake. Without ultrasound, however, carbonation extent was reduced with MgCl2 addition. The benefit of MgCl2 under sonication can be linked to the preferential formation of aragonite (85 wt% of formed carbonates), which precipitates on the slag particles in the form of acicular crystals with low packing density, thus becoming more susceptible to the surface erosion effect of sonication, as evidenced by the significantly reduced carbonated slag particle size
Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments
We provide evidence that the obliquities of stars with close-in giant planets
were initially nearly random, and that the low obliquities that are often
observed are a consequence of star-planet tidal interactions. The evidence is
based on 14 new measurements of the Rossiter-McLaughlin effect (for the systems
HAT-P-6, HAT-P-7, HAT-P-16, HAT-P-24, HAT-P-32, HAT-P-34, WASP-12, WASP-16,
WASP-18, WASP-19, WASP-26, WASP-31, Gl 436, and Kepler-8), as well as a
critical review of previous observations. The low-obliquity (well-aligned)
systems are those for which the expected tidal timescale is short, and likewise
the high-obliquity (misaligned and retrograde) systems are those for which the
expected timescale is long. At face value, this finding indicates that the
origin of hot Jupiters involves dynamical interactions like planet-planet
interactions or the Kozai effect that tilt their orbits, rather than
inspiraling due to interaction with a protoplanetary disk. We discuss the
status of this hypothesis and the observations that are needed for a more
definitive conclusion.Comment: Accepted for publication in ApJ; typos corrected, 2 broken references
fixed, 26 pages, 25 figure
Spitzer Reveals Evidence of Molecular Absorption in the Atmosphere of the Hot Neptune LTT 9779b
Non-rocky sub-Jovian exoplanets in high-irradiation environments are rare. LTT 9779b, also known as Transiting Exoplanet Survey Satellite (TESS) object of interest (TOI) 193.01, is one of the few such planets discovered to date, and the first example of an ultrahot Neptune. The planet's bulk density indicates that it has a substantial atmosphere, so to investigate its atmospheric composition and shed further light on its origin, we obtained Spitzer InfraRed Array Camera secondary eclipse observations of LTT 9779b at 3.6 and 4.5 μm. We combined the Spitzer observations with a measurement of the secondary eclipse in the TESS bandpass. The resulting secondary eclipse spectrum strongly prefers a model that includes CO absorption over a blackbody spectrum, incidentally making LTT 9779b the first TESS exoplanet (and the first ultrahot Neptune) with evidence of a spectral feature in its atmosphere. We did not find evidence of a thermal inversion, at odds with expectations based on the atmospheres of similarly irradiated hot Jupiters. We also report a nominal dayside brightness temperature of 2305 ± 141 K (based on the 3.6 μm secondary eclipse measurement), and we constrained the planet's orbital eccentricity to e < 0.01 at the 99.7% confidence level. Together with our analysis of LTT 9779b's thermal phase curves reported in a companion paper, our results set the stage for similar investigations of a larger sample of exoplanets discovered in the hot-Neptune desert, investigations that are key to uncovering the origin of this population
Spitzer Reveals Evidence of Molecular Absorption in the Atmosphere of the Hot Neptune LTT 9979b
Non-rocky sub-jovian exoplanets in high irradiation environments are rare.
LTT 9979b, also known as TESS Object of Interest (TOI) 193.01, is one of the
few such planets discovered to date, and the first example of an ultra-hot
Neptune. The planet's bulk density indicates that it has a substantial
atmosphere, so to investigate its atmospheric composition and shed further
light on its origin, we obtained {\it Spitzer} IRAC secondary eclipse
observations of LTT 9979b at 3.6 and 4.5 m. We combined the {\it Spitzer}
observations with a measurement of the secondary eclipse in the {\it TESS}
bandpass. The resulting secondary eclipse spectrum strongly prefers a model
that includes CO absorption over a blackbody spectrum, incidentally making LTT
9979b the first {\it TESS} exoplanet (and the first ultra-hot Neptune) with
evidence of a spectral feature in its atmosphere. We did not find evidence of a
thermal inversion, at odds with expectations based on the atmospheres of
similarly-irradiated hot Jupiters. We also report a nominal dayside brightness
temperature of 2305 141 K (based on the 3.6 m secondary eclipse
measurement), and we constrained the planet's orbital eccentricity to at the 99.7 \% confidence level. Together with our analysis of LTT
9979b's thermal phase curves reported in a companion paper, our results set the
stage for similar investigations of a larger sample of exoplanets discovered in
the hot Neptune desert, investigations which are key to uncovering the origin
of this population.Comment: 12 pages, 5 figures; accepted to ApJ Letter
TKS X: Confirmation of TOI-1444b and a Comparative Analysis of the Ultra-short-period Planets with Hot Neptunes
We report the discovery of TOI-1444b, a 1.4- super-Earth on a
0.47-day orbit around a Sun-like star discovered by {\it TESS}. Precise radial
velocities from Keck/HIRES confirmed the planet and constrained the mass to be
. The RV dataset also indicates a possible
non-transiting, 16-day planet (). We report a tentative
detection of phase curve variation and secondary eclipse of TOI-1444b in the
{\it TESS} bandpass. TOI-1444b joins the growing sample of 17
ultra-short-period planets with well-measured masses and sizes, most of which
are compatible with an Earth-like composition. We take this opportunity to
examine the expanding sample of ultra-short-period planets () and
contrast them with the newly discovered sub-day ultra-hot Neptunes
(, TOI-849 b, LTT9779 b and K2-100). We find that
1) USPs have predominately Earth-like compositions with inferred iron core mass
fractions of 0.320.04; and have masses below the threshold of runaway
accretion (), while ultra-hot Neptunes are above the threshold
and have H/He or other volatile envelope. 2) USPs are almost always found in
multi-planet system consistent with a secular interaction formation scenario;
ultra-hot Neptunes (1 day) tend to be ``lonely' similar
to longer-period hot Neptunes(1-10 days) and hot Jupiters. 3) USPs
occur around solar-metallicity stars while hot Neptunes prefer higher
metallicity hosts. 4) In all these respects, the ultra-hot Neptunes show more
resemblance to hot Jupiters than the smaller USP planets, although ultra-hot
Neptunes are rarer than both USP and hot Jupiters by 1-2 orders of magnitude.Comment: Accepted too AJ. 12 Figures, 4 table
TESS delivers its first Earth-sized planet and a warm sub-Neptune
The future of exoplanet science is bright, as TESS once again demonstrates
with the discovery of its longest-period confirmed planet to date. We hereby
present HD 21749b (TOI 186.01), a sub-Neptune in a 36-day orbit around a bright
(V = 8.1) nearby (16 pc) K4.5 dwarf. TESS measures HD21749b to be
2.61 , and combined archival and follow-up
precision radial velocity data put the mass of the planet at
. HD 21749b contributes to the TESS Level 1
Science Requirement of providing 50 transiting planets smaller than 4
with measured masses. Furthermore, we report the discovery of HD
21749c (TOI 186.02), the first Earth-sized () planet from TESS. The HD21749 system is a prime target for
comparative studies of planetary composition and architecture in multi-planet
systems.Comment: Published in ApJ Letters; 5 figures, 1 tabl
Transits of Known Planets Orbiting a Naked-Eye Star
© 2020 The American Astronomical Society. All rights reserved.Some of the most scientifically valuable transiting planets are those that were already known from radial velocity (RV) surveys. This is primarily because their orbits are well characterized and they preferentially orbit bright stars that are the targets of RV surveys. The Transiting Exoplanet Survey Satellite (TESS) provides an opportunity to survey most of the known exoplanet systems in a systematic fashion to detect possible transits of their planets. HD 136352 (Nu2 Lupi) is a naked-eye (V = 5.78) G-type main-sequence star that was discovered to host three planets with orbital periods of 11.6, 27.6, and 108.1 days via RV monitoring with the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. We present the detection and characterization of transits for the two inner planets of the HD 136352 system, revealing radii of 1.482-0.056+0.058 R ⊕ and 2.608-0.077+0.078 R ⊕ for planets b and c, respectively. We combine new HARPS observations with RV data from the Keck/High Resolution Echelle Spectrometer and the Anglo-Australian Telescope, along with TESS photometry from Sector 12, to perform a complete analysis of the system parameters. The combined data analysis results in extracted bulk density values of ρb = 7.8-1.1+1.2 g cm-3 and ρc = 3.50-0.36+0.41 g cm-3 for planets b and c, respectively, thus placing them on either side of the radius valley. The combination of the multitransiting planet system, the bright host star, and the diversity of planetary interiors and atmospheres means this will likely become a cornerstone system for atmospheric and orbital characterization of small worlds.Peer reviewe
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